2.4 MFI sudden no start issue

regency · regency's Garage

My 73 T has been running perfect since the complete rebuilt, now about 4000 miles ago. On the last two Fridays, I took the car out for a drive in the foothills here in Northern Calif. After a quick stop, I couldn't get it to start. The 1st time, thinking my points were the problem, I messed with them but still, no start and had to call AAA. The following day, I changed the points, reset the gap and it started right up. The next day, I warmed the car up to temp, rechecked the points and timed the engine. Then had a nice ride.

Then, last Friday, took the car out to pick up some supplies for a weekend job and when I tried to start the car to go, no start, again. AAA again.
Saturday morning I rechecked everything, snapped everything back together and it started and ran fine.

Both times this happened, it was pretty warm, like about 75-80 on the parking lots that I stopped in.

The engine is 2.4 T, MFI recently rebuilt by Pacific Inj to "E", "E" cams, "E" throttle bodies, 85mm cylinders & J&E pistons, MSD & MSD coil.

GaryR · GaryR's Garage

Don't drive the car on Fridays. Sorry, had to do it..

Sounds like its cranking, is it not getting spark or gas when this happens? That would be where I would start (no pun)...

regency · regency's Garage

Yeah, it's cranking, I hear the fuel pump & I think it's a no spark issue.

And Yes, no drive this coming Friday.

GaryR · GaryR's Garage

How old is the MSD box and Coil? Sounds more like a loose connection somewhere that you touched on but could be related to heat also. Next time take it for a good ride and shut it off at home, wait 5 and try and restart. If no start pop a plug wire off and put a spare plug in and have someone crank a few revs to see if it sparks (while grounded). If it was CIS I would point to the Accumulator and the tank check valve, MFI I have no clue.

Jeff Higgins · 05-10-2010, 07:42 AM

So, this sounds like it's only an issue when the car is warm and has sat briefly. This is a very common problem with MFI. It can usually be traced back to one of just a few things.

First is operator error. What is your warm start procedure? Porsche recommends that the accelerator be floored for warm starts. I usually try it first with the accelerator at idle, and if it does not start immediately, I resort to flooring it.

Another common problem is that the thermal time switch often fails, making warm starts difficult. I finally got so frustrated with this one I took it off and wired a switch to operate the bypass solenoid for cold starting. I'm not aware of a way to test the thermal time switch - maybe someone can chime in on that.

Zeke · 05-10-2010, 09:47 AM

Quote:

Originally Posted by Jeff Higgins

So, this sounds like it's only an issue when the car is warm and has sat briefly. This is a very common problem with MFI. It can usually be traced back to one of just a few things.

First is operator error. What is your warm start procedure? Porsche recommends that the accelerator be floored for warm starts. I usually try it first with the accelerator at idle, and if it does not start immediately, I resort to flooring it.

Another common problem is that the thermal time switch often fails, making warm starts difficult. I finally got so frustrated with this one I took it off and wired a switch to operate the bypass solenoid for cold starting. I'm not aware of a way to test the thermal time switch - maybe someone can chime in on that.

I used to have to remove the center fuse at the rear electrical console (disables cold start circuit) because of flooding issues when starting warm. Same problem as yours, or similar.

Eddyvdw · Eddyvdw's Garage

I installed a by-pass switch, works for me cold and hot!
Ed

Jeff Higgins · 05-10-2010, 11:25 AM

Quote:

Originally Posted by milt

I used to have to remove the center fuse at the rear electrical console (disables cold start circuit) because of flooding issues when starting warm. Same problem as yours, or similar.

Before I wired the remote switch on the dash, I would simply unplug the wire from the bypass solenoid once the car was warm. Same idea - just disable the darn cold start so it doesn't flood the thing when it's warm.

regency · regency's Garage

Jeff, I'm using the hand throttle, full "up" while starting, I keep my right hand on the hand throttle and as soon as I get it fired, I push it down to idle. That's how I've always started the car, Is that the right way?

I too have been thinking my problem is related to the thermal time switch too.

Tell me more about installing a by-pass switch, please.

Thanks all.

Steve

graybrown · 05-11-2010, 08:13 AM

I had a really bad warm start problem with my 72T. When hot, the car would never start with the starter. I could always push start the car, though, and it fires right up. Park on an incline, get the car going about 10 MPH, put her in 2nd, pop the clutch and they usually fire right away. That's if you have the same problem I had, which was a bad engine to chassis ground and weak battery to chassis ground. Replace both ground straps and your car will start much better because it will have enough power to run the starter and the ignition. It will get much better mileage too because you will have a hotter spark.